The short answer
Monoclonal antibodies are immune system proteins made in a lab to recognize specific targets. Many are used to treat cancer, some by marking cancer cells for the immune system and others by bringing immune cells close to the cancer. They can cause side effects such as skin reactions and flu-like symptoms.
Monoclonal antibodies are immune system proteins created in the lab to recognize specific targets.
They are a type of targeted therapy, and some are also immunotherapy.
Some mark cancer cells so the immune system destroys them; others bring T cells close to cancer cells.
Many have been approved to treat a wide variety of cancers.
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The full explanation.
The simple version
Your body naturally makes proteins called antibodies. Antibodies help your immune system recognize germs that cause disease, such as bacteria and viruses. They mark those germs for destruction.
Monoclonal antibodies are immune system proteins that are created in the lab. Like your body's own antibodies, they recognize specific targets. Scientists design them to attach to targets found on cancer cells.
Monoclonal antibodies are lab-made proteins that lock onto specific targets on cancer cells.
How they fight cancer
Many monoclonal antibodies are used to treat cancer. They are a type of targeted cancer therapy. That means they are designed to interact with specific targets. Some are also immunotherapy, because they help turn the immune system against cancer.
They can work in a few different ways:
- Marking cancer cells. Some monoclonal antibodies mark cancer cells. The immune system can then recognize and destroy them more easily. One antibody, for example, binds to a protein called CD20. CD20 sits on B cells and on some cancer cells, and the binding causes the immune system to kill them. B cells are a type of white blood cell.
- Bringing T cells to the cancer. Other monoclonal antibodies bring T cells close to cancer cells. One binds to a protein on the surface of leukemia cells. At the same time it binds to a protein on the surface of T cells. That helps the T cells get close enough to respond to and kill the leukemia cells.
Which cancers they treat
Many monoclonal antibodies have been approved to treat a wide variety of cancers. Whether one is an option for you depends on your specific cancer. Your care team is the best source of information about your treatment.
Side effects to know about
Monoclonal antibodies can cause side effects, and they differ from person to person. Several things shape which ones you may have. Those are how healthy you are before treatment, your type of cancer, how advanced it is, the type of antibody, and the dose. Doctors and nurses cannot know for sure when or if side effects will occur. So it is important to know the warning signs.
Like most immunotherapy, monoclonal antibodies can cause skin reactions at the needle site and flu-like symptoms.
Needle site reactions include pain, swelling, soreness, redness, itchiness, and rash.
Flu-like symptoms include chills, fatigue, fever, muscle aches and pains, nausea, vomiting, and diarrhea.
Less common but serious reactions
Monoclonal antibodies can also cause more serious problems. Those include mouth and skin sores that can lead to infections. They also include high blood pressure, congestive heart failure, heart attacks, and inflammatory lung disease.
They can cause mild to severe allergic reactions while you are receiving the drug. In rare cases, a reaction is severe enough to be life-threatening.
Some can cause capillary leak syndrome. In it, fluid and proteins leak out of tiny blood vessels into nearby tissues. That causes dangerously low blood pressure. Cytokine release syndrome can also occur, though it is often mild. Cytokines are immune substances. A sudden rise in their levels can cause fever, nausea, headache, rash, rapid heartbeat, low blood pressure, and trouble breathing.
Because reactions can happen during or after treatment, tell your care team right away if you feel unwell.
When to get help sooner
- Call 911 or go to an emergency department if your lips, tongue or throat swell, breathing turns difficult, or you feel faint during or soon after a dose. Allergic reactions to these drugs are usually mild, but a small number are life-threatening.
- Call 911 or go to an emergency department if a pounding heartbeat, faintness or a fast spreading rash begins in the hours after treatment. That mix is how cytokine release syndrome tends to start.
- Speak to your cancer team the moment it starts, day or night, if you get a fever or shaking chills after a dose. A fever during cancer treatment is treated as a medical emergency in CDC's guidance, because infection can move fast when your counts are low. If you cannot reach them quickly, go to an emergency department and tell them you are on cancer treatment.
- Call your care team the same day if you feel unusually tired, achy or nauseated in the days after a dose, or a mild rash appears without fever.
- Call your care team within a day or two if sores appear in your mouth or on your skin, the needle site stays red and painful, or home blood pressure readings run higher than they used to.
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Common questions
What are monoclonal antibodies?
Monoclonal antibodies are immune system proteins that are created in the lab. Your body naturally makes antibodies that help the immune system recognize germs and mark them for destruction. Like your own antibodies, monoclonal antibodies recognize specific targets.
How do monoclonal antibodies treat cancer?
They are a type of targeted therapy designed to interact with specific targets. Some are also immunotherapy. For example, some mark cancer cells so the immune system recognizes and destroys them, and others bring T cells close to cancer cells to help the immune cells kill them.
Are monoclonal antibodies the same as targeted therapy?
Monoclonal antibodies are a type of targeted cancer therapy, which means they are designed to interact with specific targets. Some monoclonal antibodies are also considered immunotherapy because they help turn the immune system against cancer.
Which cancers do they treat?
Many monoclonal antibodies have been approved to treat a wide variety of cancers. Your care team can tell you whether one is an option for your specific cancer.
What are common side effects?
Like most immunotherapy, monoclonal antibodies can cause skin reactions at the needle site (such as pain, swelling, redness, itchiness, or rash) and flu-like symptoms (such as chills, fatigue, fever, muscle aches, nausea, vomiting, and diarrhea).
Can monoclonal antibodies cause serious reactions?
Yes, though this is less common. They can cause mild to severe allergic reactions while you receive the drug, and in rare cases a reaction is severe. They can also cause other serious problems, so it is important to know the warning signs and tell your team if you have problems.
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Sources last checked: 2026-08-13 what this meansLast updated: 2026-08-18Next planned review: 2027-01-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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